Method and an arrangement for filing a silo

ABSTRACT

A method and an apparatus for filling a silo ( 1 ) with a fluidizable material. The arrangement includes conveying devices ( 5, 9 ) for supplying material to an upper area of the silo and a central material distributor ( 10 ). The material distributor includes a tank ( 29 ) which has an inlet ( 28 ) and one or more distributor pipes ( 26, 26 ′) for distributing material to one or more feed units ( 11, 11 ′)which convey the material down towards the surface of the material in the silo.

BACKGROUND OF THE INVENTION

1. Filed of the Invention

The present invention concerns a method and an arrangement for filling asilo.

2. Description of Related Art

In industries in which large quantities of fluidizable material arehandled, for example oxide for the aluminium industry, segregationproblems arise with the current systems. Such segregation means thatlocal variations can arise with regard to the accumulation of thematerial's lower (finer) and upper (coarser) fractions. The segregationis initiated during the filling operation, in which large movements ofair can easily occur in the silo with consequent accumulation of finerfractions, depending on the geometry of the silo, particularly out bythe silo's walls. During emptying or removal of mass from the silo,there can subsequently be problems with varying fractions, which, inturn, can also result in operational disturbances downstream of the silosuch as blockages in the silo and accompanying transport systems.Operational disturbances in the silo itself or downstream of the silocan result in an increased possibility of discharge of fine dust to theenvironment. In connection with the production of aluminium, suchoperational disturbances can result in undesired situations in the cellswith sludge formation, anode damage, blockage of point feeders, etc. sothat the cells have to be “opened” to implement various measures, withan increased risk of the emission of heat and fluoride gases to theenvironment.

DE-U1-9408840 discloses a storage silo having a material distributorcentrally located at the top part of the silo. The distributor comprisesa container with a centrally top-mounted inlet through which material isfed into the container, and a centrally arranged outlet in its bottomtogether with outlets in its sides. The outlets in the sides of thecontainer are connected with air slides for the transport of materialsto inlet openings arranged in the top part of the silo. Inside thecontainer there is arranged a ring member below the centrallytop-mounted inlet. The ring member is of limited vertical extensionallowing materials to flow both beneath its lower edge and above itsupper edge to the outlets in the sides of the container. The centrallyarranged outlet is operated by a closing valve while transport out ofthe outlets can be operated by activating the air slides by fluidizinggas. By filling the silo in an alternating manner either through thecentrally arranged outlet of the container or through the outlets in thesides of the container via the air slides to the inlet openings in thetop part of the silo, batches of material of different qualities can bedistributed over the cross-sectional area of the silo thus resulting ina mixing of different fraction sizes in the filling procedure of thesilo. However, problems related to air induced segregation will still bepresent in this solution, in particular under filling operations at lowmaterial levels in the silo, i.e. under conditions where the fallingheight of the material will be high.

Attempts are usually made to avoid operational disturbances as a resultof air-induced segregation in a silo by not emptying the silocompletely. During operation, such measures mean that the problemsassociated with segregation are postponed as the silo graduallyaccumulates so much fine material that it must come out in one way oranother. The options for removing it are then either to empty the silocompletely and remove the fine material or to use it in the process withthe risk of operating problems.

The following article, “An anti-segregation tube to counteract aircurrent segregation”, by Are Dyrøy and Gisle G. Enstad, pages 27-30,POSTEC Newsletter No. 16, December 1997, proposes a method forcounteracting segregation during the filling of a silo using a centralpipe (filling pipe) which extends from the top of the silo down to itsbottom. The pipe is equipped with valves along its full length which areclosed until filling begins. When the silo is filled, the lowest valveopens because the pressure inside the pipe is greater than that outsidethe pipe. In connection with the upper part of the pipe, it is possibleto mount an inlet lock to prevent air accompanying the material withwhich the pipe is filled and to regulate the quantity fed into the pipe.This solution has proved to be effective in counteracting segregationwhen filling a silo.

A restriction of the arrangement described above is that the pipe, whichis mounted centrally in the tank, will be exposed to large forces fromthe material with which the silo is filled. A further restriction isthat it is difficult to use the full capacity of the silo with thisarrangement as the angle of slip of the material will prevent completefilling out by the walls of the silo. Moreover, there may be a need foradditional deaeration with the proposed system in order to avoidsegregation on account of high air speeds during filling, in particularin connection with the handling of material which has previously beenfluidized, i.e. material which contains air from prior upstreamtransport.

SUMMARY OF THE INVENTION

The present invention attempts to avoid the above problems. The presentinvention is based on the quantity of air which is fed into the siloduring filling being kept to a controlled, minimal level. The presentinvention also causes the actual material which is fed into the silo tobe distributed in a favorable manner and allows the silo to be filledmore quickly. Furthermore, the present invention represents anarrangement which is more robust with regard to the stresses caused bylarge material movements such as slips in the silo.

BRIEF DESCRIPTION OF THE INVENTION

The present invention will be described in the following in furtherdetail using the accompanying figures and examples, in which:

FIG. 1 shows an arrangement for filling a silo in accordance with thepresent invention; and

FIG. 2 shows a section (seen from above) through a silo with anarrangement for filling a silo in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a silo 1 with a bottom 2 and side walls 3. An arrangement 4for filling the silo is mounted in the upper part of the silo. Avertical conveyor 5 brings material from a store 6 up to a deaerationbox 7, from where a deaeration pipe 8 returns to the store. From thedeaeration box 7, the material is conveyed via a conveyor 9, for examplea fluidized channel or a horizontal conveyor of any type, to a centralmaterial distributor 10. One or more (two are shown in the figure) feedunits 11, 11′, comprising an inlet regulator or inlet lock 12, 12′ andfilling pipe 13, 13′, may be connected to the material distributor. Theinlet lock and filling pipe may be, but are not restricted to being, ofthe same type as stated in the above “POSTEC” article. In the figure,the inlet lock comprises a fluidizing element 14, 14′, an outlet 15,15′, an inlet 16, 16′ and de-aeration pipe 17, 17′. The filling pipe 13may comprise one or more valves 18, 19 and have any cross-sectionalform, square, circular, etc. The inlet lock and filling pipe are notdescribed in detail here as they are not objects of the presentinvention.

The inlets 16, 16′ are in connection with distributor pipes 26, 26′respectively. The distributor pipes may include slightly slopingchannels, for example with an angle of 1-3°, and may comprise one ormore fluidizing elements 26 a, 26 a′ to the bottom of which compressedair or gas is supplied (not shown). The distributor pipes 26, 26′ areconnected to outlets 27, 27′ at the material distributor 10. Thematerial distributor shown in the figure includes a tank 29, which ispreferably cylindrical. However, other geometrical forms may also beused, for example a parallelepipedic form. The tank 29 comprises aninlet 28 in its upper part through which material can be fed in from thehorizontal conveyor 9. At its lower part or bottom 20, the tank showncomprises a fluidizing element 30, which fully or partially covers thebottom. The fluidizing element is connected to a source of compressedair or gas (not shown). The bottom of the tank is provided with acentral outlet 32, which may expediently have a valve 31 for emptyingthe tank for inspection, service, etc. The bottom may expediently beconical towards the outlet and have an angle of 7°. For deaeration(removal of air) of the material which enters the tank 29, the tank isprovided expediently with one or more deaeration pipes 37, 38. Thesepipes are preferably located in the upper part of the tank andcommunicate with the surrounding air. The pipes are open at their endsand may extend downwards towards the bottom of the silo. Alternatively,the pipes may be connected to the store 6.

As shown in FIG. 1, a central element 36 is mounted in the tank 29 tocontribute to uniform distribution of the material when it is fed intothe tank. The element 36 may comprise an upper, conical funnel device33, which is designed to lead the material down into a pipe 34, which ispreferably a cylindrical pipe. As the figure shows, the pipe 34 ends alittle above the bottom 20 of the tank so that an annular opening isformed between the end of the pipe and the bottom 20. The annularopening is designed to cause material which enters the tank via thefunnel device 33 and the pipe 34 to be distributed uniformly outwards inboth a radial and a circumferential direction and upwards from thebottom of the tank. The flow of the material in the area between thepipe 34 and the bottom 20 is indicated with lines 35 in the figure.

The method of operation of the material distributor 10 is as follows.

The material is fed into the material distributor 10 at the inlet 28 ofthe tank 29 by means of the conveyor 9. The material is fed into thetank through the funnel device 33 and pipe 34 and is distributed outover the tank bottom 20. The material is fluidized (made to behave likea fluid) by means of the fluidizing element 30, and the material levelin the tank 29 will rise uniformly throughout the annulus formed betweenthe inner wall of the tank 29 and the outer wall of the pipe 34. Whenthe level reaches the outlets 27, 27′, the material will flow into thedistributor pipes 26, 26′ in roughly equal quantities and out into thefeed units 11, 11′.

If more material is fed into the distributor 10 than the feed units 11,11′ can feed into the silo, in terms of capacity, or if the silo hasbeen filled up so that the feed units 11, 11′ are full, the distributorpipes 26, 26′ will be blocked by material. In the tank, the level in theannulus between the pipe 34 and the wall of the tank will then riseuntil the level balances out the level inside the pipe 34. These twolevels may be different. The difference in level will depend inparticular on the geometrical dimensions which define the annulusbetween the pipe 34 and the wall of the tank, the opening between thelower part of the pipe 34 and the bottom 20 and the dimensions of thepipe. These dimensions should be chosen expediently so that the level inthe annulus cannot rise above the level where the aeration pipes 37, 38are mounted. In this situation, the pipe 34 will be filled right up tothe inlet 28. As a safety measure, the aeration pipes may serve asoverflows, i.e. if the filling level should exceed the design criteria,the material can be discharged via the aeration pipes 37, 38.

Depending on the type of conveyor 9 chosen, this will also graduallybecome full. In this situation, the vertical conveyor will begin toconvey as much material down as it conveys up or it may stop. Such astoppage can be brought about, if, for example, a vertical conveyordriven by an electric motor is used, by any increase in the motor loadbeing monitored and a stop switch being activated if the load exceedsnormal load. A person skilled in the art will be able to implement suchmeasures and, consequently, they will not be described in further detailhere. The horizontal conveyor may be fitted with equipment to monitorload, filling level, etc.

As shown in FIG. 1, the silo itself may also be fitted with means forcontrolled deaeration. For example, the silo may have intakes 40, 40′for surrounding air and outlets 41, 41′ for the removal of air from thesilo. The outlets may be connected to the store 6 and may comprise meansof extraction such as fans (not shown). A cyclone or similar arrangement(not shown) may be mounted in connection with the material distributorfor further deaeration of the material which is fed into the silo. Theintakes and outlets may comprise valves which can be controlled inrelation to measured pressure conditions in the silo and may also becontrolled by means of a preprogrammed control unit. When using the feedprinciple on which the present invention is based, it is important tocontrol the pressure conditions and to make the material feed asairtight as possible so that air-induced segregation can be restrictedoptimally.

Although, in the example described, two distributor pipes and two feedunits are shown, the present invention is not restricted to thesenumbers. Therefore, constellations of any number of feed units will fallwithin the scope of the present invention. For example, the materialdistributor may have six distribution pipes distributed uniformly in thesilo, preferably at its wall and distributed uniformly along itscircumference at equal angular intervals (60°). Regardless of the choiceof number of feed units, they should be located symmetrically around thecenter of the silo. This is because the formation of heaps in the siloshould take place symmetrically to distribute the load uniformly (amongother things on the base of the silo) and to prevent slides or slipswhich can damage the silo or the feed units. For maximum protection, thefeed units should be located out at the wall of the silo or as close toit as practically possible. In this way, any slides will move away fromthe feed units and in towards the center of the silo, which means thatthe feed units can be dimensioned for lower maximum stress than if theywere located more centrally in the silo.

FIG. 2 shows a section (seen from above) through a silo 1 with anarrangement for filling the silo in accordance with the presentinvention. In this embodiment, six feed units 11, 11′, 11″, 11′″, 11″″,11′″″ are mounted, with associated distributor pipes 26, 26′, 26″, 26′″,26″″, 26′″″, connected to the material distributor 10. As shown in thefigure, each distributor pipe 26 can have a branch 50, which comprises achannel or a pipe which ends open towards the inner space of the silo alittle way out from the distributor pipe. The function of the branch 50is to direct material directly down into the silo if required, forexample if the feed unit for the associated distributor pipe should failor if the silo is full in the area of the feed unit. The branch ispreferably mounted so that it is located approximately half a radiusfrom the center of the silo. Moreover, the branch may have a fluidizingelement which is activated by a level monitor mounted at an appropriatelocation in the adjoining feed unit. If the level monitor in the feedunit emits a signal which indicates that the feed unit is full, thefluidizing element in the branch 50 is activated so that material isconveyed from the branch down into the silo. In this state, thefluidizing element in the inlet lock 12 is still active while afluidising element (not shown) located in the distributor pipe betweenthe branch and the inlet lock is rendered inactive until the levelmonitor no longer indicates that the feed unit is full. With this typeof control, the silo will be filled in a controlled manner and therewill be a high utilization rate of the volume. Any segregation, whichmay occur by the material being fed into the silo from the branch, is sominimal using this method, in particular on account of the low fallheight, that it can be ignored.

Moreover, the device described can advantageously be retrofitted in oldsilos, even silos with unfavorable geometry with regard to thepossibility of air-induced segregation, so that these silos can,therefore, be operated with a lower level of segregation than waspreviously possible.

It should be understood that the material distributor 10 may serveplural silos. In such an arrangement the distributor may be located inthe vicinity of the silos at an appropriate height where distributorpipes 26 feed material to each silo.

What is claimed is:
 1. An apparatus adapted to fill a silo with afluidizable material, said apparatus comprising: means for conveying thematerial by pneumatic transport to an upper area of the silo; an annularcentral material distributor including a tank having an inlet and atleast one outlet; at least one feed unit having an inlet for receivingthe material from said central material distributor, and an outlet forfeeding the material in a downward direction toward the bottom of thesilo; and at least one distributor pipe extending from said tank outletof said central material distributor and said inlet of said at least onefeed unit.
 2. The apparatus as claimed in claim 1, wherein said tankincludes a fluidizing element arranged centrally at the bottom of saidtank.
 3. The apparatus as claimed in claim 2, wherein said inlet of saidtank communicates with a pipe mounted in a center of said tank, saidpipe opens downwardly so as to form an annular opening between a lowerend of said pipe and said fluidizing element at the bottom of said tank.4. The apparatus as claimed in claim 1, wherein said distributor pipecomprises a sloping channel and at least one fluidizing element on asurface of said channel.
 5. The apparatus as claimed in claim 1, whereinsaid distributor pipe comprises a branch through which material can beconveyed directly down towards the bottom of the silo.
 6. The apparatusas claimed in claim 1, wherein said feed unit and said central materialdistributor are provided with deaeration means.
 7. The apparatus asclaimed in claim 1, wherein said feed unit includes a filling pipeextending toward the bottom of the silo, and said filling pipe includesat least one valve.
 8. An apparatus adapted to fill a silo with afluidizable material, said apparatus comprising: a conveyor whichconveys the material by pneumatic transport to an upper area of thesilo; a central material distributor disposed in the upper area of thesilo, said central material distributor including a tank having an inletand a plurality of outlets; an annular plurality of feed units disposedadjacent an upper interior wall of the silo, wherein each of said feedunits has an inlet for receiving the material from said central materialdistributor, and an outlet for feeding the material in a directiontoward the bottom of the silo; and a plurality of distributor pipes,wherein each of said distributor pipes is connected to one of said tankoutlets and to one of said feed unit inlets.
 9. The apparatus as claimedin claim 8, wherein said tank includes a fluidizing element arrangedcentrally at the bottom of said tank.
 10. The apparatus as claimed inclaim 9, wherein said inlet of said tank communicates with a pipemounted in a center of said tank, and said pipe opens downwardly so asto form an annular opening between a lower end of said pipe and saidfluidizing element at the bottom of said tank.
 11. The apparatus asclaimed in claim 8, wherein each of said distributor pipes comprises asloping channel and at least one fluidizing element provided on saidchannel.
 12. The apparatus as claimed in claim 8, wherein saiddistributor pipe comprises a branch through which material can beconveyed directly down towards the bottom of the silo.
 13. The apparatusas claimed in claim 8, wherein said conveyor is provided with adeaeration unit.
 14. The apparatus as claimed in claim 13, wherein saidfeed unit and said central material distributor are each provided with adeaerator.
 15. The apparatus as claimed in claim 8, wherein each of saidfeed units includes a filling pipe extending toward the bottom of thesilo and having at least one valve.
 16. A method for filling a silo withfluidizable material, by pneumatic transport the method comprising:conveying the material to a central material distributor disposed in anupper part of the silo, wherein the central material distributorincludes an annular tank having an inlet and at least one outlet;distributing the material towards an interior wall of the silo, from thecentral material distributor by means of one or more distributor pipesto one or more feed units wherein each of the feed units has an inletfor receiving the material from the central material distributor and anoutlet for feeding the material in a direction toward the bottom of thesilo; and distributing the material from the one or more feed units downtowards the surface of the material above a bottom of the silo.
 17. Themethod as claimed in claim 16, wherein a plurality of feed units areused, and the material is distributed uniformly between the feed unitsfrom the central area of the silo.
 18. The method as claimed in claim16, further comprising removing air or gas that is contained in thefluidizable material, while leaving a minimal amount before the materialis conveyed to the central area of the silo.
 19. The method as claimedin claim 16, further comprising conveying material from the one or moredistributor pipes at a location between the central area of the silo andthe one or more feed units so that the material at this location isconveyed directly down towards the bottom of the silo.